[LTER-sbc_help] Forest Science News - April 2019

[Hubbard Brook Research Foundation]

A monthly roundup of research headlines  Forest Science News is brought to you by the Hubbard Brook Research Foundation. April 2019 INVASIVE SPECIES The relationship between tree diversity and invasive pests? It’s complicated. Nonnative pests are a significant threat to forest ecosystems. Chestnut blight, for example, decimated the American chestnut throughout its range in the early 1900s, while the emerald ash borer and hemlock woolly adelgid are continuing to expand their North American ranges. In order to prevent future invasions, ecologists are working to understand the factors that enable exotic pests to become established. To that end, researchers paired a dataset of 130,210 forest plots with a dataset of county-level pest occurrences across the United States. They found that pest diversity was highest when tree diversity ranged from 30 to 35 species. When tree species were more or less diverse, the number of pests declined—creating a hump-shaped graph. They hypothesize that more tree species increase pests’ odds of survival to a certain point, but once there are too many hosts, the pests became isolated from one another. There seem to be many factors affecting invasions, but these results could help scientists identify and monitor forests at high risk.  Abstract: Proceedings of the National Academy of Sciences Press Release: North Carolina State University STREAMWATER CHEMISTRY There’s more nitrate in Northeastern forest streams than anyone realized Nitrate is a form of nitrogen that can be used by plants and microbes. But when nitrate moves through forest systems too quickly, it can bypass biological uptake and wind up in streams and lakes instead. Scientists measured water chemistry in the Northern Forest region of the United States and Canada and found that more nitrate is present in streams than previously thought. Nitrogen is essential to biological productivity, but too much of it causes pollution. The authors link the excess nitrogen in forest streams to industry, energy production, transportation, and agriculture.   Abstract: Environmental Science & Technology Press Release: USDA Forest Service Northern Research Station FOREST REGENERATION Human-made stressors are creating “regeneration debt” in northeastern forests Researchers from the University of Maine and the National Park Service analyzed data from 18 states, from South Carolina to Maine, to understand how development, invasive species, and growing deer populations are impacting forest regeneration. They found that some species are failing to regenerate in the mid-Atlantic region. The “regeneration debt,” the authors warn, could have wide-ranging impacts—trees that would otherwise find suitable new habit further north as the climate warms may be unable to migrate beyond the barriers they face in the mid-Atlantic.  Abstract: Journal of Applied Ecology Press Release: The University of Maine Reflecting on Harvard Forest’s experimental hurricane, 30 years later In March 2019, Harvard Forest celebrated 30 years as a Long Term Ecological Research site—a program funded by the National Science Foundation for studying long-term and large-scale phenomena. One of the very first projects Harvard Forest initiated under the LTER designation was both long-term and large-scale: Scientists pulled down 279 trees to mimic hurricane damage in an experimental plot and have been meticulously measuring the forest’s recovery ever since. They’ve found that the forest has recovered surprisingly well. The amount of leaf litter in the damaged plot returned to normal after just six years, and the species composition has remained fairly stable. Growth in the experimental plot has yet to catch up with the surrounding area, but researchers will continue to monitor regeneration, among other forest characteristics, in the years to come. Article: Harvard Gazette HUBBARD BROOK HIGHLIGHT How does lichen composition change with elevation? Lichens are often used as indicators for air pollution and other human-induced environmental changes because of their high sensitivity to their environments—these complex organisms absorb nutrients as well as pollutants from the atmosphere. Researchers at the Hubbard Brook Experimental Forest set out to test whether the composition of lichen communities within the forest is more influenced by atmospheric pollution or by moisture; both tend to increase with elevation gain.    They sampled twelve plots between 480 and 900 meters of elevation and identified 68 different lichen species, including twelve regionally rare species and four that had not been documented in New Hampshire before. The distribution pattern of the lichens suggests that pollution is not currently restricting which lichen species occur in the forest, though the legacy of acid rain in the region does seem to have affected the current species composition. The lichen at Hubbard Brook do seem to be responding to the higher availability of moisture at greater elevations, leading the authors to question whether optimal moisture conditions could help lichen overcome the effects of certain types of air pollution.  Abstract [full PDF behind paywall]: The Journal of the Torrey Botanical Society The above links were curated from news articles and press releases published during March 2019. The Hubbard Brook Research Foundation is a nonprofit organization dedicated to supporting the Hubbard Brook Ecosystem Study Forest Science News is a science communication tool designed to improve communication between ecosystem scientists and public audiences in the northeastern U.S. and eastern Canada. 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